[Hospital standardised mortality ratios do not with certainty reflect the quality of patient care]

Hospital standardised mortality ratios (HSMRs) are presumed to reflect an overall quality of patient care in hospitals. Figures for all Danish hospitals are being published quarterly on the Internet, and aggregated values are used to set goals for both regional and nationwide efforts to improve quality of care and patient safety. We have analysed the available data from 2007 through 2011 and cannot reconcile the quite substantial and often sudden changes in HSMRs with changes in quality of care, but believe that they are due to inherent noise in calculating HSMRs, e.g. owing to variable quality of the diagnostic coding.